Power-driven fluid pump



5, 1952 R. F. WORLIDGE 2,605,707

POWER-DRIVEN FLUID PUMP Filed May 4, 1946 3 Sheets-Sheet l Aug. 5, 1952 R. F. WORLIDGE 2,605,707

POWER-DRIVEN FLUID PUMP Filed May 4, 1946 5 Sheets-Sheet 2 g- 5, 1952' R. F. WORLIDGE 2,605,707

POWER-DRIVEN FLUID PUMP Filed May 4, 1946 t 3 Sheets-Sheet 3 Patented Aug. 5, 1952 Ronald Frederick Worlidge, London, England Application May 4, 1946, Serial No. 667,405 In Great Britain August 4, 1944 Section 1, Public Law 690, August s, 1946 Patent expires August 4, 1964 The present invention relates to power driven fluid pumps and is especially but not exclusively concerned with hydraulic fluid pumps suitable for operating aircraft or similar hydraulic systems.

The pumpis of the kind operated in two stages by two pumping units driven by a common shaft,

said units acting in succession on the working vfluid, and the second stage pumping unit being a piston pump having one or more radial cylinders whose pistons are operated on their working stroke by a cam or eccentric with which they are held in contact by the pressure of the fluid supplied to them by the first stage unit, which may be of the gear pump type.

In accordance with the invention the output of the pump is controlled by controlling the output pressure of the first stage (thereby varying the effective stroke of the second stagepistons) zero output being obtained by reducing the output pressure of the first stage to below the minimum required to restore the second stage pistons. This minimum pressure will normally be determined by the pressure required to open the spring loaded inlet valves of the second stage cylinders.

The output of the pump may be automatically' and progressively controlled in accordance with'variations in the output pressure by applying that pressure to a valve which when a predetermined delivery pressure is reached opens and relieves the interstage pressure.

Alternatively the first stage pressure may be relieved back to its delivery side by a valve which is mechanically operated. The mechanical operating means may be actuated manually or in accordance with the movement of a member operated by the output of the pump. For example, if the pump. is used to supply actuating fiuid to a hydraulic ram, mechanical coupling means may be provided whereby upon the ram reaching the limit of its travel the relief valve will be opened, thus off loading the second stage and reducing the output of the pump to zero.

According to a further important feature of the invention the first stage of the pump has a capacity considerably exceeding that of the second stage, so that under high altitude flying conditions, notwithstanding the reduction in efficiency of the first stage by a high vacuum on its inlet side, it will still be able to supply the second stage to its full capacity, so that the efiicient working of the pump will not be impaired.

In the preferred construction the first stage deliversto the second stage through non-return valves, whilst the second stage discharges 1 Claim. (01. 103-5) 2 through'non-return valves to the pump delivery outlet, whereby any desired delivery and pressure may be obtained in accordance with the speed of rotation of the shaft. Preferably also the first'stage'pumping unit is of the gear pump type r In the construction example of pump according to the invention hereinfater described and'il lushated the fiuid to be pumped is fed to, or drawn two gears in mesh, one driver and one driven,

the said gears being enclosed in a casing so .formed that when the gears are rotatedfiuid is passed-round in the teeth from one side 'to the other; the fluid is then fed by this first stage to the second stage which consists of one or a number of pistons, so'arranged that each piston can be forced in one direction only by rotating a cam or eccentric crank. Y The motive power required to move the pistons in the opposite direction to that imposed .by the cam or eccentric is supplied entirely by the fluid, delivered under pressure by the first stage of the pump, acting on the said pistons, and. by so arranging non-return valves between the pistons and the first stage delivery, and also between the pistons and the outlet from the pump, the secondstage can be caused by simultaneously'rotating'ithe driving gear of the first stage Landcam or eccentric of the second stage :to deliver fluid at any desired pressure.

The pump also includes .a valve which is'so arranged that when the output pressure oi the second stage reaches a predetermined maximum, it acts upon. the .said valve in such a manner as to cause it to move against a spring or other resisting force and so pass fluid-from the delivery of the first stage, either to drain, or .tozthe inlet of the first stage thus reducing, either wholly or in part, the pressure at WhiChfflUl'd is being delivered by the first stage, and by so doing removing either completely, or in part, the motive power necessary to move the pistons of the second stage in the direction opposite to that imposed by the rotating cam or eccentric. The pistons will therefore be moved to one end-of their travel by the rotating eccentric, but will fail, either completely or .in part, .to make the return stroke necessary to maintain continuous pumping; thus the output of the second stage will be reduced, due to the reduction in the stroke of the pistons, to a quantity which may be zero or between zero and the maximum capacity which is determined by the size and full normal stroke of -the piston or pistons.

alternatively to a drain connection 40.

of Figure 1 with the cylinder block removed, and

looking in the direction of the arrow II;

Figure 3 is an end elevation with the left hand cover plate removed, in the plane Q, Q of Figure 1, looking in the direction of the arrows;

Figure 4 is in part a cross-sectional view in the plane A-A of Figure l and in part an elevation with the right hand cover plate removed, in the plane X-X of Figure 1 looking in the direction Y-Y.

Figure is a longitudinal section on the line B -C of Figure 2, with the cylinder block not sectioned and Figure 6 is a plan viewof the pump.

Referring to the drawings the pump comprises an outer casing formed by a cylindrical body I closed at its ends by right and left hand cover plates 2 and 3 respectively, which carry the roller bearings 4 for the inner end of the pump shaft 5 and 6 for the outer portion of shaft 5. On the outer side of bearing 6 the shaft 5 is encircled by a sealing device I to prevent any escape of liquid from the interior of the pump.

Within the cylindrical body I is a partition 8 which carries an intermediate roller bearing 9 for the shaft 5 and divides the interior of the pump body into two chambers. The left hand chamber contains the gear pump unit and the right hand chamber contains the piston and cylinder pump unit. The body I and the cover plates 2 and 3 are held in assembly by a number of peripherally spaced bolts ID.

'The gear pump unit comprises a pair of intermeshing gears II and I2, of which the gear II is mounted on shaft 5 and the gear I2 is mounted eccentrically on a spindle I 3 supported at its ends by cover plate 3 and partition 8. The two gears I I and I2 rotate in circular recesses cut in the pump body'l and the oil or other working fluid admitted at inlet opening I4 is conducted to the 'gear pump and admitted to a space I5 on one side of the gears I! and I2. After passing through .the gears and developing a pressure dependent *upon' their rotation, the oil passes into a space which communicates through a port I6 with an annulus [8 on the opposite side of partition 8, leading on the one hand to the valve I! and on the other hand to the inlet valves 24 of the piston pump unit.

The valve I7 is disposed between cover plate 3 and partition I}, and the annulus l8 communicates' through port 35 with the chamber below the valve H (see Fig. 5). The part of the valve chamber above the valve I! communicates through passage 31 in cover plate 3. with the part annular passage 36 leading to the space I5 on the suction .or inlet side of the gear pump unit or The operation and function of valve I! will be hereinafter explained in detail.

On the right hand side of partition 8 in Figure 1 the cylinder block [9 fits into the casing I. This block is bored radially to receive a plurality of cylinders 20 in which slide pistons 2|. These pistons make peripheral contact with an eccentric cam ring 22 mounted on the shaft 5 through the intermediary of a needle roller bearing 23.

The supply of oil to the cylinders 29 and its discharge therefrom is controlled by double valves fitted into bores in the cylinder block I9 between the cylinders. The said valves comprise an inlet valveportion 24 and an outlet valve portion 25 which are controlled by springs 25 between the two valves and a spring 27 acting on the outlet valve 25. The inlet valve 24 controls a port communicating with annular passage I8 and the outlet valve 25 controls a port leading into discharge annulus 23 which leads to delivery outlet 29 (Fig. 6). In the bore in which the double valve 24, 25 moves is a port which communicates through passage 38 with th interior of an adjacent cylinder 20. As the pistons 2| reciprocate in cylinders 21] the oil enters the cylinders through valves 24 and passages 39 and leaves the cylinder through the same passages 3e and outlet valves 25. Rubber or other packing rings 38 and 39 are provided between the cylinder block i9 and the cover plate 2 to reduce internal leakage.

On their outward or working strokes the pistons 2! are positively driven by the eccentric 22, and instead of being restored to their radially inward position by non-working strokes produced by springs or the like, the pistons 2! are forced inwardly simply by the pressure of the oil entering the cylinders 28 from the gear pump or first stage unit of the pump.

Thus the pressure attained in the first stage of the pump is used to load the pistons against the driving power of the eccentric 22. This arrangement renders it possible to reduce the output of the pump to zero by reducing wholly or in part the pressure which loads the pistons 2| against the driving eccentric 22, thus reducing the effective stroke or" the pistons by restricting the return stroke which the pistons are able to make before the eccentric 22 again forces them outwards on the next working stroke. The delivery will be reduced to zero but maximum pressure is attained when the first stagepressure applied to the pistons 2I approaches zero, so that the pistons 2I perform no inward strokes at all and therefore also no outward or delivery strokes.

The above action results from the use of the interstage valve I? already referred to. This is a poppet type of valve the underside of whichis subject to the piston loading pressure produced by the first stage of the pump, which reaches it through passage if, annulus I8 and port 35. This pressure acts on the annular surface surrounding the valve stem, whilst the delivery pressure of the pump produced by its second stage, acts on the end of the valve stem. This delivery pressure reaches the end of the valve stem through a passage 3i (Figures 2 and 4 and indicated in dotted lines in Figure 5) passing through the cylinder block is from the delivery annulus 28, and the radial passage 32 (Figure 2). The movement of the valve under the action of these pressures is controlled by the double spring arrangement comprising the weak spring 33 and the strong spring 3 3 acting on the head of the valve in a direction contrary to the oil pressure. These springs are sufficiently strong to maintain a certain maximum first stage pressure, but the addition of the delivery pressure to the valve stem reduces the required pressure from the first stage and with an increasing delivery pressure .a decreasing first stage pressure will result.

'livered by the second stage 7 less or until the delivery pressure of the second stage is so reduced that the aforementioned J pressure of the first stage in relation to the delivery pressure and thus control the loading pressure of the second stage pistons by means of the delivery pressure, which, when it reaches a predetermined value, is able to hold the valve ll wide open with no assistance from the first stage pressure; thus the first stage pressure is permitted to flow back to the suction side of the first stage at a pressure which is insufficient to open I the inlet valves 24 of the second stage. Any surplus oil delivered by the second stage pistons during the final part of their operation escapes to suction through ports ie when valve H is fully opened by the delivery pressure acting on the end of the stem. It will be seen that the position of these ports 60 controls possible opening of the valve ll. Consequently, thecylinders do not fill and no movement of the pistons 2| radially inwards for subsequent outward movement by the eccentric ring takes place. At intermediate delivery pressures the loading of the springs 33 and 34 will be required to be borne to a greater extent by the first stage pressure and the resultant pressure in the annulus 58 may then be suficient partially to open the inlet valves 2:3, and drive the pistons the maximum springs 33 and 34 are able to close the valve ll, thus raising the delivery pressure of the first stage, and reapplying the motive force, either wholly or in part, for the return stroke of the pistons 2!.

As already indicated, it is not essential to the controlled in accordance with variations in the output pressure; the output pressure of the first 2| inwardly tov a reduced extent, so that the working stroke of the pistons is reduced and the delivery correspondingly reduced. v

Preferably the first stage of the pump is given at least twice the capacity of the second stage, so that when flying at high altitudes the efliciency of the first stage may be reduced, by reduction of its inlet pressure, by 50% without starving the second stage, thus improving the efficient working of the pump as a whole. The 50% of remaining capacity will be sufficient to both operate and supply the second stage to full capacity. By this means high altitude conditions up to some 40,000 feet can be accommodated without the necessity for pressurising the pump inlet by a separate device and without unduly increasing the prior consumption of the pump, since the maximum first stage pressure is only some 10 to 12 of the final delivery pressure.

a relatively small percentage.

It will be understood, of course, that the delivery pressure will be dependent upon the load on the pump 1. e. will be high when the load is high, and low at small loads. When the load is zero, the delivery pressure will be zero, and the first stage output will be maximum, whereas when the load is maximum the delivery pressure will be maximum and the first stage pressure will be minimum, thereby reducing the delivery to zero. Under this last condition of running the power taken by the pump will be almost zero since the delivery will be zero although the pressure is maintained. I

Having completed the aforementioned se- Therefore an increase in" capacity will only reduce the overall efiiciency by will not increase unstage may instead be relieved by a mechanically operated valve. In such cases the construction of the pump may be precisely as above described and as shown in the accompanying drawings except for the means provided to actuate the relief valve ll. The channel 3i by which the output pressure is applied to this valve is omitted and means are provided for mechanically opening the valve, these means being actuated either manually'or by a member which is operated by the output of the pump.

Ihe invention claimed is:

A two stage power driven fluid pump comprising a casing, a partition in said casing dividing same into a first chamber and a second chamber, a pump shaft extending through said chambers, means for admitting a working fluid to said first chamber, a gear pump unit in said first chamber including intermeshing gears actuated by said shaft toimpart to said fluid a pressure dependent upon the speed of rotation of said gears, means for discharging the fluid output of said gears from said first chamber into said second chamber, a piston pump in said second chamber including a plurality of cylinders disposed radially of said shaft, pistons in said cylinders,

' means on said shaft for actuating said pistons in the fluid pressures in said chambers to control the output pressure or" said first chamber and thereby control the volume of fluid supplied to said cylinders and thus the effective stroke of said pistons. V

RONALD FREDERICK WORLIDGE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,022,556 Johnson et al. Apr. 9, 1912 1,349,005 Pfefier Aug. 10, 1920 1,770,297 Bussman July 8, 1930 1,886,393 Godfriaux Nov. 8, 1932 1,936,935 Fitch et al. Nov. 28, 1933 1,971,601 Dilg Aug. 28, 1934 1,978, Svenson Oct. 30, 1934 Ernst Sept. 13, 1938 

